Interfacial plasticity mediated by lath boundaries in reduced-activation ferritic/martensitic steels

•The onset lath boundary sliding sensitively depends on the microscopic structure of the interfacial planes.•The lath boundary sliding is mediated by the motion of dislocation arrays lying on the interfacial plane.•For predominant lath boundary sliding:-The Burgers vector of the interfacial dislocations must lie on the interfacial plane.-The interfacial plane must be parallel to the common slip planes in the BCC structure, i.e., {110}. In the hierarchically-arranged crystallographic structure of reduced-activation ferritic/martensitic (RAFM) steel, the smallest but the most abundant microstructural unit, i.e., the lath, plays an important role in dislocation plasticity. Due to the multi-scale complexity in the lath-martensitic microstructure, miniaturized mechanical characterization at very fine scale is required to understand the deformation mechanism associated with laths. In this study, uniaxial micro-compression tests combined with rigorous crystallographic analysis were performed to figure out the plastic deformation mechanism of lath boundary sliding in RAFM steels. These experimental results were further interpreted via molecular dynamics simulations to discover the underlying dislocation mechanisms. We found that the amount of lath boundary sliding is controlled by the crystallographic orientation of the lath boundary plane, the direction of Burgers vectors of the interfacial dislocations, and the magnitude of resolved shear stress on the lath boundary plane. Also, the effect of normal stress on the lath boundary plane was investigated. [Display omitted]